Method for fracture of material in situ with stored inertial energy

ABSTRACT

An earth working apparatus is provided with means for storing large amounts of inertial energy and means for cyclically delivering the energy on demand by impact means to a rock fracturing work tool. The energy is stored in a large flywheel and delivered by suitable transmission means to the work tool.

United States Patent 1191 1111 3,897,975

Cobb et al. 1 Aug. 5, 1975 [54] METHOD FOR FRACTURE ()F MATERIAL 3.293.778 12/1966 McAuliff l. 172/41) X [N SITU w STORED INERTIAL ENERGY 3.367.716 2/1968 Bod ne 4 r 299/14 3.437.381 4/1969 Bodlne l 299/14 X [75] Inventors: Delwin E. Co Carl L. K pn r. 1443.327 5/1969 Martin 172/40 x both of Peoria; Wayne E. Roberts, 3.633.683 1/1972 Shatto 299/14 X Pekin; Albert L, Woody, Peoria all 3.645.021 2/1972 Sonerud .1 37/141 T of I11.

[73] Assignee: Caterpillar Tractor Co., Peoria. 111. Primary Elwm-m,r EmeSt Pursar [22] Filed: Aug. 27, 1973 Attorney. Agent. or Firm-Phil1ips. Moore,

Weissenberger Lempio & Strabala [21] Appl. No; 377.324

Related US. Application Data [62] Division of Ser. No. 133,262. April 12. 1971, Pat.

No 3.770.322. 1 1 ABSTRACT [52] US. Cl. 299/14 An earth working apparatus is provided with means [51] Int. Cl. r. AOlB 35/00; EOlC 23/09 for storing large amounts of inertial energy and means [58] Field of Search. 299/14. 37; 37/141 R. 141 T, for cyclically delivering the energy on demand by im- 37/1175. DIG. 18; 172/40 pact means to a rock fracturing work tool. The energy is stored in a large flywheel and delivered by suitable [56] References Cited transmission means to the work tool UNITED STATES PATENTS 3.238.646 3/1966 Oldenburg H 37/141 R 5 Claims. 29 Drawing Figures weer/3975 PATENTED M19 51975 SHEET qm m PATENTEI] RUB 5 I975 SHEET fi m wa PATENTEU G 5 I975 SHEET PATENTED MIG W5 SHEET PATENTED 5 I975 SHEET UH IJ PAIENT U AUG 51975 1 897, 975

SHEET 7 PATENTEI] M113 51975 SHEET loioioq X PATENTED RUB 51975 SHEET PATENTEU AUG 5 I975 SHEET PATENTEU AUG 5 i975 SHEET METHOD FOR FRACTURE OF MATERIAL IN SITU WITH STORED INERTIAL ENERGY This is a divisional of our co-pending application Ser. No. 133,262 filed Apr. 12, [971 and now U.S. Pat. No. 3,770,322, entitled Apparatus for Fracture of Material in Situ With Stored Inertial Energy.

BACKGROUND OF THE INVENTION This invention relates to earth moving and fracturing implements and pertains more particularly to a method employing high energy mechanical apparatus for the storage and intermittent instantaneous delivery of high levels of energy for the fracturing or separation in situ of hard rock and other earth materials or the like.

A considerable amount of hard rock must be fractured yearly for the construction and mining industries. Most of this rock today is fractured by drilling with percussion or rotary drills and blasting with dynamite or ammonium nitrate. This technique is expensive, slow, noisy and dangerous.

Mechanical tractor drawn rippers have been developed which will operate efficiently in relatively soft, weathered, fissured, layered or previously blasted rock. However, such rippers will not operate in hard rocks.

One of the major problems with the use of rippers is the high forces that must be induced in rock and similar hard material to cause it to fracture. This necessitates the delivery of very high force and energy to the face of the rock or other material to be fractured or separated. Vehicles capable of delivering such forces statically would of necessity be enormous in size and cost and would thus be impractical.

Many exotic techniques have been proposed for fracturing earth formations. Such proposed techniques in clude sonic energy, electrical spark, water cannon, and others. Such techniques have shown the ability to fracture rock formations but have proven in most cases inefficient for commercial application.

One such sonic technique is the employment ofa resonant vibratory system. This system stores vibratory energy in a spring which may take many forms. The energy is then cyclically delivered to a vibrating tool at the resonant frequency of the system. The major problem with this system is that a spring large enough to store adequate energy would be too large to be practical. Another problem is that frequency is critical and varies with load such that there is a major problem of control.

Other proposals have been made to apply vibratory energy to an earth working implement. Such proposals have generally met with failure for one reason or another.

Air and hydraulic hammers are impractical because of their low efficiency. Such large amounts of energy are required to vibrate a tool for breaking rock that unreasonably large amounts of input power would be required.

The present invention is based on the application of the theory that a dynamic system is desirable for cutting and breaking rock and other materials since large forces can be produced with a small average thrust. This is an important feature when the average thrust is limited by tractive effort and weight of a vehicle.

The average force will be proportional to the time the force is applied. For example, if 100,000 lb is applied for one-tenth of a second every second, the needed average force will be only 10,000 lb. The basic idea is to put the desired force on and unload again as quickly as possible so that during most of the cycle the force is zero or small. if this can be done the average force, compared to the peak force, will be small. if it is as sumed that the work done in breaking rock does not depend on the rate of loading, then the total work and average power will not be affected by this pulse type of loading.

The peak power requirements, however, will be large if the work is done in short pulses. This means that large amounts of energy have to be available to be released quickly when needed. For a flywheel-crank system most of the energy is stored as kinetic energy in the flywheel. For a vibrating mass-spring system, the energy cycles back and forth from potential energy in the spring to kinetic energy of the mass. In either case, the force that can be developed by the tool is limited by the stored energy.

Large amounts of energy have to be available to produce large forces quickly. The reason for this is that the tool has to penetrate into the rock or soil before the needed force can be developed. If the rock or soil were rigid, little energy would be required. But since they act much like a spring, energy has to be released in order to develop the required force. As an example, assume that a tool in rock has a spring rate of 6 X 10 lb/in. and the breaking force is 6 X 10 pounds. In this case, 30,000 in lb of energy will be needed to break out a chip. If this is done at a frequency of 20 times a second then 9l horsepower will be required.

In the subject invention as applied to a ripper, the work that the ripper performs is of an intermittent nature, taking place only during a small part of the time required for the driving shaft of the ripper to make a complete revolution. Since the material being fractured is extremely hard, the instantaneous demand of the rippers exceeds that of the drive motors. Therefore, a flywheel or flywheels are placed on the drive shaft to store sufficient energy to meet peak demands. During a greater part of the revolution of the driving shaft, the motor power is used to accelerate the speed of the flywheel. During the part of the revolution when the work is done, the energy thus stored up in the flywheel is given out at the expense of its velocity. As the velocity of the flywheel changes, the energy it will absorb or give up is proportional to the difference between the squares of its initial and final speeds and is equal to the difference between the energy which it would give out if brought to a full stop and that which is still stored in it at the reduced velocity. Hence E Energy release (ft. lbs) I Movement of inertia of rotating mass in lb. ft. sec.

W Weight (lbs) G Gravity 32.2 ft./sec./sec. at sea level K Radius of gyration in feet N Revolutions per minute (RPM) before any energy has been given out N Revolutions per minute (RPM) at end of period during which energy has been given out m Angular velocity radian/sec. before any energy is given out in Angular velocity radian/sec. at end of period during which energy has been given out W K is a measure of the energy potential of a flywheel system in lb.-ft. at a given RPM and can be determined by the formula This formula is a derivative of the above formula for energy.

Extensive computer and soil bin model tests have been conducted on the subject concept as applied to a ripper. A model impact ripper has been built and tested in various rock materials to determine the feasibility of fracturing hard rock with an impact device constructed in accordance with the present invention. The performance criterion for the model was specific energy, and is defined as the amount ofenergy (in-lbs.) required to fracture a unit volume (in?) of rock. Specific energy permits one to determine the amount of power necessary to obtain a given production (yd./hr.) in a certain rock material. The specific energy of rocks vary. The specific energy is calculated according to the following equation:

where S. E. Specific energy (in.-lb./in.

N Number of impacts during a run D Density of rock (I lb./in.

W Weight of rock removed during a run (lbs) E Average Energy per blow (in.lbs.)

It should be noted that the parameters must be considered collectively with a unique relationship existing between one another. The specific energy of the material being fractured is a significant factor.

With a steel spring of the type needed in a resonant system (a ripper shank, bar, spring), the maximum amount of potential energy that can be stored in a cubic inch of spring material is:

where S is the maximum axial stress that the material can endure and E is the modulus of elasticity. For a working stress of 40,000 psi of a spring material then, the stored energy will be (4 X l) /[(2) (30 X 80/3 26.7 in.lb./inc. In a vibrating system using a column of uniform cross section for example, the maximum stored energy will be one-half of this value since the column will not be uniformly fully stressed throughout its length.

In contrast, a flywheel can store much more energy than this per cubic inch of steel. Use a thin annular ring rotating about its polar axis as an example. The tangen tial stress in the rotating ring is given by the equation:

S w r n In this case, w is the mass density of the ring, r is the radius, and n is the angular velocity. The kinetic energy in the ring due to its velocity will be:

K.E. l n V2wVr n A V5 Where V is volume of ring V l in.

K.E. A S 20,000 in.lb. for S 40,000 psi The ratio between flywheel and spring energies is, therefore at least: 20,000/13.35 or 1500 to I. In other words, I500 times more energy can be stored in the flywheel than in an equivalent amount of steel spring for a given stress level. In addition, the stress in the spring is fully reversed each cycle, while the stress in the flywheel at most goes from zero to the maximum value. Reversing the stress in the spring energy cycle can adversely affect the fatigue life of the spring.

In order to work the above ring at 40,000 psi, the flywheel would have to be quite large or else rotate at a high speed. If the speed is limited to I200 rpm with a wheel radius of 15 in. and a resulting stress of only 2600 psi, the energy in a cubic inch of the steel ring will be 1300 in.-lb. for an energy ratio of about 100. This is less than the I500 ratio, but it is still a substantially significant advantage.

For breaking rock in situ in quantity, large forces and power are required. This means large energies per blow and many blows per minute. The prior art systems have been unable to meet these requirements.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide an earth working method that is effective, efficient and overcomes the above disadvantages of the prior art.

Another object of the present invention is to provide an earth working method that includes storing large amounts of energy and selectively applying it to an earth working implement.

A further object of the present invention is to provide a method employing a dynamic system that is capable of delivering sufficient energy to a tool for rock breaking to be practical.

A still further object of the present invention is to provide a method employing a mechanical dynamic system that is capable of efficiently delivering high energy pulses to a rock breaking tool.

In accordance with the present invention, there is provided a method including the steps of storing large amounts of inertial energy in a massive flywheel and cy' clically delivering the energy by impact to an earth working implement at peak power demand. Suitable transmission means including a crank and impact means is provided to transmit the energy to an earth working implement such as a ripper.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view partially in section of a rock ripper incorporating a preferred embodiment of the present invention; 

1. A method of fracturing a rock formation, said method comprising the steps of: mounting a ripper shank on a frame for oscillatory movement relative thereto; manipulating the fracturing tip of said ripper shank into engagement with a surface of a rock formation; storing rotary inertial energy in a massive balanced rotating flywheel by continuously rotating said flywheel; transmitting portions of said energy on demand to said shank in the form of high energy impact blows by the further steps of, translating the rotary motion of said flywheel to oscillatory motion by eccentric means, positioning impact means adjacent said shank for intermittent engagement therewith, and interconnecting said eccentric means and said impact means by means of rigid means journaled for rotation on said eccentric means for establishing a positive connection of said eccentric means to said impact means for imparting movement of said impact means intermittently into engagement with said shank.
 2. The method of claim 1 wherein said inertial energy is sufficient to prevent more than a 10 percent variation in the angular velocity of said flywheel during transmission of said energy to said shank; and, said step of transmitting said energy to said shank is carried out by impact means operatively connected to said flywheel by means of a crank and a link.
 3. The method of claim 2 wherein the step of manipulating said ripper shank is carried out by means of a movable frame mounted on a mobile vehicle and includes positioning and maintaining said fracturing tip into engagement with said surface at an angle thereto; and, said step of transmitting energy to said shank is carried out so that said energy is delivered thereto at said angle.
 4. The method of claim 3 wherein said angle is between 15* and 55* and is a function of the hardness of said rock formation.
 5. The method of claim 4 comprising the further step of adjusting the frequency of said impact blows to the motion of said shank into engagement with said formation to maintain a high velocity ratio of said implement to the speed of said shank into said formation. 